Vibrants are very good. Pypes M80 fit also. You want stainless body, 2.5 inch straight through design in a 4 inch case. You can also find some 3.5 inch case resonators, but they will do a little less sound reduction. I run one pair of Vibrant 12 inch and one pair of Top Speed ebay resonators (which are 3.5 inch case). I think the Vibrant are higher quality. You can buy them on Amazon for about $50 each.